make update messages work if a key is missing (#2998)

* add a test for unencrypted replies to encrypted webxdc instances

* make update messages work if a key is missing

even in opportunistic chats,
replies to encrypted messages are forced to be encrypted,
if that is not possbile, message sending fails.

while this is okay to not leak previously send text messages,
the quotes as used by webxdc are more artificial,
currently only the static text "Webxdc".

* changelog ...

CHANGELOG.md

@@ -35,7 +35,7 @@
 - sql: enable `auto_vacuum=INCREMENTAL` #2931
 - Synchronize Seen status across devices #2942
 - Add API to set the database password #2956
-- Add webXdc #2826
+- Add Webxdc #2826 #2998
 
 ### Changed
 - selfstatus now defaults to empty

src/webxdc.rs

@@ -251,6 +251,7 @@ impl Context {
                     .ok_or_else(|| format_err!("Status object expected."))?,
                 );
                 status_update.set_quote(self, Some(&instance)).await?;
+                status_update.param.remove(Param::GuaranteeE2ee); // may be set by set_quote(), if #2985 is done, this line can be removed
                 let status_update_msg_id =
                     chat::send_msg(self, instance.chat_id, &mut status_update).await?;
                 Ok(Some(status_update_msg_id))
@@ -450,8 +451,10 @@ impl Message {
 mod tests {
     use super::*;
     use crate::chat::{
-        create_group_chat, forward_msgs, send_msg, send_text_msg, ChatId, ProtectionStatus,
+        add_contact_to_chat, create_group_chat, forward_msgs, send_msg, send_text_msg, ChatId,
+        ProtectionStatus,
     };
+    use crate::contact::Contact;
     use crate::dc_receive_imf::dc_receive_imf;
     use crate::test_utils::TestContext;
     use async_std::fs::File;
@@ -1349,4 +1352,57 @@ sth_for_the = "future""#
 
         Ok(())
     }
+
+    #[async_std::test]
+    async fn test_webxdc_opportunistic_encryption() -> Result<()> {
+        let alice = TestContext::new_alice().await;
+        let bob = TestContext::new_bob().await;
+
+        // Bob sends sth. to Alice, Alice has Bob's key
+        let bob_chat_id = create_group_chat(&bob, ProtectionStatus::Unprotected, "chat").await?;
+        add_contact_to_chat(
+            &bob,
+            bob_chat_id,
+            Contact::create(&bob, "", "alice@example.org").await?,
+        )
+        .await?;
+        send_text_msg(&bob, bob_chat_id, "populate".to_string()).await?;
+        alice.recv_msg(&bob.pop_sent_msg().await).await;
+
+        // Alice sends instance+update to Bob
+        let alice_chat_id = alice.get_last_msg().await.chat_id;
+        alice_chat_id.accept(&alice).await?;
+        let alice_instance = send_webxdc_instance(&alice, alice_chat_id).await?;
+        let sent1 = &alice.pop_sent_msg().await;
+        let update_msg_id = alice
+            .send_webxdc_status_update(alice_instance.id, r#"{"payload":42}"#, "descr")
+            .await?
+            .unwrap();
+        let update_msg = Message::load_from_db(&alice, update_msg_id).await?;
+        let sent2 = &alice.pop_sent_msg().await;
+        assert!(alice_instance.get_showpadlock());
+        assert!(update_msg.get_showpadlock());
+
+        // Bob receives instance+update
+        bob.recv_msg(sent1).await;
+        let bob_instance = bob.get_last_msg().await;
+        bob.recv_msg(sent2).await;
+        assert!(bob_instance.get_showpadlock());
+
+        // Bob adds Claire with unknown key, update to Alice+Claire cannot be encrypted
+        add_contact_to_chat(
+            &bob,
+            bob_chat_id,
+            Contact::create(&bob, "", "claire@example.org").await?,
+        )
+        .await?;
+        let update_msg_id = bob
+            .send_webxdc_status_update(bob_instance.id, r#"{"payload":43}"#, "descr")
+            .await?
+            .unwrap();
+        let update_msg = Message::load_from_db(&bob, update_msg_id).await?;
+        assert!(!update_msg.get_showpadlock());
+
+        Ok(())
+    }
 }